Abstract: A receiver for receiving a reception signal defining a measured value is connected to a two-wire transmission line used for transmitting a digital command signal from a communicator, a digital measured value signal from a transmitter, and a response signal responding to the command signal. The receiver includes a timer for discriminating that a nonsignalling state of the two-wire transmission line has continued for a predetermined period, and a CPU for validating a specific period of a reception signal received after the discrimination operation of the timer.

Abstract: A method of digital process variable transmitter calibration includes the steps of sensing the process variable (PV) to produce an analog output which is converted to a digital signal representation. The digital signal is corrected by a microprocessor using a characterization equation previously individually developed during a manufacturing testing of the process variable transmitter over a predetermined range of environmental stimuli to ascrtain the coefficients for a polynomial in the form of PV=A.sub.o =A.sub.1 P+A.sub.2 +. . . A.sub.i P.sup.i. Thus, the digital computer produces a process variable representation as a modified digital output. Subsequently, the digital output from the computer is converted to a conventional 4-20 mA analog signal for use as a process control signal.

Abstract: A method of digital temperature compensation uses a digital temperature compensation word to produce a digital word modification of a digital input to a temperature sensitive digital to analog converter hereinafter converter. The method includes the steps of sensing the temperature affecting the converter to produce a digital temperature representation which is used by a digital computer to produce an output in accordance with a characterization equation in the form of Output=f(D, M) where D=digital data and M=f(temperature). The temperature stability of the converter is affected by the temperature stability of a reference voltage circuit used in the converter and having a voltage reference diode. A compensation circuit uses a temperature sensor in the form of a second diode, which is thermally coupled to the reference diode, and a tracking type analog-to-digital converter for converting an analog signal.

Abstract: A variable gain amplifier is adjusted to maintain its amplification within a linear range, i.e., to prevent saturation of the amplifier, by utilizing the output of an analog-to-digital converter, which is arranged to convert an analog output of the amplifier to a digital representation, by a digital computer to effect the gain change of the amplifier. Concurrently, the output signal of the digital computer representing the output signal from the analog-to-digital converter is modified to produce a system output signal based on a constant overall gain of the system which is equivalent to the highest available gain from the amplifier. Thus, while the amplifier gain is adjusted by the computer in response to the amplitude of the input signal, the overall system gain is maintained at a level which would be available at the highest amplifier gain. The digital output of the system can subsequently be utilized as a control signal either directly or after a digital-to-analog conversion.

Abstract: The operating range for a process variable transmitter used as a pressure transmitter is selectively non-interactively adjusted by successively applying upper and lower range values (URV and LRV) of input pressure to produce an LRV output signal and calculating the URV and the Span which is equal to the difference between the upper and lower range values, i.e., URV-LRV, to produce outputs from the transmitter representing the new upper and lower range values corresponding to the calculated Span.